Visual light communication (VLC)/Dark light communication (DLC) is a preferred communication technique over Radio Frequency (RF) communication because of its high bandwidth and immunity to interference from electromagnetic sources. VLC refers to a visual illumination source which in addition to illumination can send information using the same light signal. The revolution in the field of solid state lighting leads to the replacement of florescent lamps by Light Emitting Diodes (LEDs) which further motivates the usage of VLC.
VLC(s) are an emerging form of communications that use visual forms of light emitters to communicate data wirelessly. VLC uses a light source that is frequency modulated, or uses a light source that is turned on and off rapidly when transmitting a communication. VLC systems employ visible light for communication that occupy the spectrum from 380 nm to 750 nm corresponding to a frequency spectrum of 430 THz to 790 THz. The low bandwidth problem in RF communication is resolved in VLC because of the availability of the large bandwidth. The VLC receiver only receives signals if they reside in the same room as the transmitter, therefore the receivers outside the room of the VLC source will not be able to receive the signals and thus, it has the immunity to security issues that occurs in the RF communication systems. As a visible light source can be used both for illumination and communication, therefore, it saves the extra power that is required in RF communication. Inherent features of VLC include high bandwidth, no health hazard, low power consumption and non-licensed channels that made it attractive for practical use.
Some of the applications using VLC are: Light Fidelity (Li-Fi); Vehicle to vehicle communication; Underwater communication; Hospitals; Information displaying signboards; Visible light identification (ID) system; Wireless local area networks (WLANs), Dimming; etc.
VLC-enabled LED luminaires, in addition to infrared (i.e., non-visual or DLC)-enabled luminaires, and synchronization protocols have enabled inexpensive white LEDs to be time division multiplexed to avoid packet collisions during communication. Luminaires use token message passing to regulate packet transmission.
Fundamentally, modulating light requires changes of light intensity. For the last century, incandescent lamps have been the primary source of light, but incandescent light cannot comply with high speed modulation because of the mechanism it uses to generate light. Incandescence is the effect of emitting thermal radiation from matter as a result of its temperature. In an incandescent light bulb, a wire is heated by running a current through it, and the resistance of this wire forms kinetic energy which is released in the form of light. This means that intensity control of incandescent lamps takes place through at least two steps (i.e., heating the wire and releasing light in the form of heat energy), resulting in indirect control of the signal. This would not be a problem if the thermal inertia would not make the system too slow for high speed modulation, but it does.
VLC/DLC light is typically transmitted in all directions and a receiver must be able to see multiple light transmitters at the same time in larger and more complex systems. Further, the receivers are required to handle mesh network conditions, which drops the capacity of a communication system. For at least the above reasons, VLC/DLC devices, systems, and methods that limit at least one of the receiver or transmitter are needed. In an aspect, the devices, systems, and methods may enhance or maximize the information bandwidth for a VLC/DLC communication system.